1. Field of the Invention
The present invention relates to a method and system for short message transmission by using the DECT data communications system.
2. Description of the Prior Art
For short-range data transfer, e.g. inside buildings, it is known to use cordless paging and telephone systems, like those according to CEPT CT1 and CEPT CT2 standards. However, these kind of systems do not usually provide transfer of data in text form, the so called short messages. Further, it is not possible to transfer short messages between the system and the public telenetwork.
To be used mainly for speech transmission there are cordless mobile phone systems like NMT (Nordic Mobile Telephone System) and GSM (Global System for Mobile Communications). These are meant as long-range communication networks. The digital GSM-system also provides short message transmission. The GSM-system has been described in the following publication, i.a.: M.Mouly, M-B.Pautet: The GSM System for Mobile Communications, 1992.
In the GSM system the short messages are transmitted through the short message service center SC. The mobile terminated short messages (SM-MT) are transferred from the short message service center through the short message gateway mobile services switching center SMS-GMSC and the GSM mobile services switching center MSC to the mobile station MS (FIG. 1). In the mobile station the short message can be stored in the memory of the SIM card (Subscriber Identity Module) or the mobile station (MS). Mobile originated short messages (SM-MO) are transferred along the respective transmission path to the short message service center SC transmitting the short message further to the desired address.
Short message transfer does not require establishment of an end-to-end traffic path between the mobile station and the short message service center. The mobile station can send and receive short messages even during a call or when it is not in a state for receiving calls.
FIG. 2 illustrates protocols and protocol layers used in short message transfer of the GSM system. There are four layers in the short message service protocol structure: lower layers, short message relay (SM-LR), short message transfer (SM-LT) and application layer (SM-AL). The short message transfer protocol SM-TP, short message relay protocol SM-RP and short message control protocol SM-CP are used for the transfer of short messages.
The control protocol SM-CP is used between the mobile services switching center MSC and the mobile station MS and it is a part of the connection management layer CM. Its purpose is to carry the information of the upper layers. There are three messages used: {CP-DATA}, {CP-ACK} and {CP-ERROR}.
Also the relay protocol SM-RP is used between the mobile switching center and the mobile station. The protocol data units PDU are carried in the user data field of the control protocol SM-CP. The purpose of the SM-RP protocol is to manage references and addresses. There are four messages used: {RP- DATA}, {RP-SMMA}, {RP-ACK} AND {RP-ERROR}. The {RP-SMMA} is a signal of a released short message memory.
The short message transfer protocol SM-TP is an end-to-end protocol used between the service center SC and the mobile station MS. It includes the following messages: {SMS-DELIVER}, {SMS-SUBMIT}, {SMS-COMMAND}, {SMS-STATUS-REPORT}, {SMS-SUBMIT- REPORT} and {SMS-DELIVERY-REPORT}. SM-TP layer information is carried in the user data fields of the {RP-DATA} and {RP-ERROR} messages of the SM-RP layer. {RP-DATA} may contain {SMS DELI-VER}, {SMS-SUBMIT}, {SMS-COMMAND} and {SMS-STATUS-REPORT} SM-TP layer massages whereas {RP-ERROR} may contain {SMS-SUBMIT-REPORT} and {SMS-DELIVERY-REPORT} messages. {SMS-DELIVER} is used in mobile terminated short message transfer and {SMS-SUBMIT} in mobile originated short message transfer. These messages are used for delivering the short message data. The lower layers are responsible for delivery of the acknowledgements.
The short message service of the GSM system is described in more detail in the following publications:
Recommendation GSM 04.11 Version 4.7.0: Poit-to Point Short Message Service Support on Mobile Radio Interface, European Telecommunications Standards Institute/TC-GSM, 1994, 114 pages,
Recommendation GSM 03,40 Version 3.5.0: Technical Realization of the Short Message Service--Point-to Point, European Telecommunications Standards Institute/TC-GSM, 1993, 100 pages.
The above mentioned mobile service systems work on a wide area and because of the wide range there is a rather restrictic amount of radio channels to be used. Therefore it is not profitable to use these systems at short range, e.g. for a cordless data transmission inside a building.
For the cordless communications at short range it has been developed the so called DECT system (Digital European Cordless Telecommunications), a cordless data/voice transmission system that provides profitable data/voice transfer means for calls. However, a disadvantage of this system is that transfer of short messages is not provided.
The structure of the cordless telecommunications system DECT is described in more detail in the following publication: European Telecommunication Standard ETS 300 175 1-9: Radio Equipment and Systems (RES); Digital European Cordless Telecommunications (DECT) Common Interface, European Telecommunications Standards Institute, 1992.
So, with reference to what has been stated above, by the technique of prior art it is not possible with reasonable costs to establish a cordless, short-range data transmission system, that would provide point-to-point short message transfer as well within the system as between the system and an external data transfer network like public telenetwork.